This invention relates to a table saw, particularly to one having a transmission device capable to maintain a fixed tension when the saw blade is moved up or down.
A conventional transmission device of a table saw, as shown in FIGS. 1 and 2, includes a rotatable circular saw blade 11 provided in the center of a table 10 for cutting off wood materials passing therethrough. The circular saw blade 11 is directly driven to rotate by a motor 12 fixed in a box, transmitted by a belt 13. The circular saw blade 11 must have a function of moving up and down to adapt to wood materials of different thickness. To elevate the circular saw blade 11, only turn around a hand-swinging rod 14 to let its worm 15 at a front end to activate the gear 17 under an elevating plate 16 to move, and, as the circular saw blade 11 is pivoted with the eccentric shaft hole 18 provided on an upper side of the elevating plate 16, the shaft hole 18 of the circular saw blade 11 will move in a curved direction to form different heights when the elevating plate 16 is rotating.
However, if the circular saw blade 11 arcuately moves upwards, the distance between the shaft hole 18 and the motor 12 becomes relatively long and the belt 13 is tightened. On the contrary, in case the circular saw blade 11 arcuately moves downwards, the distance between them is comparatively short and the belt 13 will become too loose to carry on transmission. Under such a condition, a spring 19 has to be additionally provided beside the motor 12 for to helping push the whole motor 12 outwards so as to permit the belt 13 to have enough tension to carry on transmission. Besides, the tension of the belt 13 is changed by the shifting of the circular saw blade 11, thus seriously affecting its service life, and the position of the spring 19 has to be adjusted to strengthen its push force after used for a period of time, resulting in increasing trouble to a user.
The main objective of the invention is to offer a transmission device of a table saw, having a motor and an elevating plate fixed on a base, a first belt connected to a belt pulley at a front end of the motor and to a transfer member, and a second belt connected to the transfer member and to the belt pulley of a circular saw blade. Thus, the first belt and the second belt are activated to rotate and carry on transmission at fixed positions, accordingly improving the trouble of the conventional device that the belt will become loose or tight when the saw blade is moving up or down.
Another objective of the invention is to offer a transmission device of a table saw, capable to keep the tension of the belts unchanged whether the circular saw blade moves up or down so as to prolong the service life of belts.